1. Technical Field
The present invention relates to a vibration gyro element using a flexing vibrating reed, and a gyro sensor and an electronic apparatus using the element.
2. Related Art
In related art, piezoelectric devices of piezoelectric vibrators, oscillators and real time clock modules with piezoelectric vibrating reeds and IC chips, etc. have been widely used as clock sources of electronic circuits for an electronic apparatus such as clocks, home appliances, various information and communication apparatuses, and an OA apparatus. Further, sensors of piezoelectric vibration gyros etc. using flexing vibrating reeds have been widely used for various electronic apparatuses such as digital still cameras, video cameras, navigation systems, vehicle position detectors, pointing devices, game controllers, cellular phones, and head-mounted displays for detection of physical quantities of angular velocities, angular acceleration, acceleration, forces, and the like.
For example, a transverse-vibration tuning bar gyro in which a piezoelectric ceramic for driving is bonded to one side surface of a vibrating arm (turning bar) having a square section and a piezoelectric ceramic for extraction is bonded to another adjacent side surface has been known (for example, see Patent Document 1 (JP-A-61-191916)). The turning bar flexurally vibrates in the X direction when a signal is applied to the piezoelectric ceramic for driving and flexurally vibrates in the Y direction by Coriolis force when rotating around the Z-axis, and thus, the angular velocity around the Z-axis may be detected from the output generated in the piezoelectric ceramic for extraction.
Further, an angular velocity sensor including a double-tuning fork vibrating reed formed by connecting two pairs of forked members as a driven pair and a sensing pair with a base has been known (for example, see Patent Document 2 (JP-A-64-31015)). It has been known that, in a vibration gyro including the double-tuning fork (H-shaped) vibrating reed, by setting a fixed relationship between the arm length and width of the vibrator and the length and width of the piezoelectric element, the second-order mode causing spurious offset output may be suppressed and highly stable detection may be performed (for example, see Patent Document 3 (JP-A-62-106314)). The vibration gyro drives and detects the vibrator using the piezoelectric element provided on the surface of the vibrator of a constant modulus alloy.
As a similar double-tuning fork vibrating reed, an angular velocity detector having two first vibrating reeds projecting from a base in the +Y direction, two second vibrating reeds projecting in the −Y direction, and a single support rod projecting from the center of the base has been known (for example, see Patent Document 4 (JP-A-10-54723)). When the first vibrating reeds vibrate in the in-plane X direction in opposite phases in the drive mode, and they rotate around the Y direction and the second vibrating reeds vibrate in the out-of-plane Z direction in the detection mode.
It has been known that, in the angular velocity sensor having the same structure as that in Patent Document 4, by determining the drive-vibration frequency and the detection-vibration frequency so that a leakage vibration may be generated in the same direction as that of Coriolis force in one vibrating reed and a leakage vibration may be generated in the opposite direction to that of the Coriolis force in the other vibrating reed, the electric signals due to the leakage vibrations are cancelled out and the detection accuracy of the angular velocity becomes better (for example, see Patent Document 5 (JP-A-9-329444)). In the angular velocity sensor, in the first vibration mode in which right and left and upper and lower vibrating reeds are horizontally and vertically opposite in phase, the third vibration mode in which the vibrating reeds are horizontally and vertically the same in phase, and the second vibration mode in which the vibrating reeds are horizontally opposite and vertically the same in phase, natural frequencies f1, f3, f2 of the respective vibration modes are set to be higher in this order by appropriately determining the dimensions of the respective parts of the H-shaped vibrator.
Furthermore, it has been known that, in the vibration gyro element, an unwanted vibration mode called a spurious mode as a fixed vibration mode different from the drive mode and detection mode is generated (for example, see Patent Document 6 (JP-A-2003-21518)). The vibration in the drive mode becomes stable by sufficiently separating the vibration frequency in the spurious mode from its vibration frequency.
A vibration gyro scope that may reduce temperature drift using the natural resonance frequency in the spurious mode has been proposed (for example, see Patent Document 7 (JP-A-2001-82962)). According to Patent Document 7, by bringing the difference Δf between the natural resonance frequency fd of the vibration in the drive mode and the natural resonance frequency fp of the vibration in the detection mode closer to 1.7 times the difference Δfs between the natural resonance frequency fd in the drive mode and the natural resonance frequency fs in the spurious mode, the temperature drift in the temperature range from −40° C. to +80° C. is significantly reduced.
Further, a vibrator of vibration gyro scope with reduced temperature drift by reducing the spurious detuning as the absolute value |fs−fd| of the difference (fs−fd) between the resonance frequency fd of the vibration in the drive vibration mode and the resonance frequency fs of the vibration in the spurious mode has been proposed (for example, see Patent Document 8 (JP-A-2004-333416)). According to Patent Document 8, the spurious detuning may be controlled by varying the masses and dimensions of the detection vibration unit and/or drive vibration unit to change the resonance frequencies in the spurious mode and/or drive vibration.
To increase the detection sensitivity in the vibration gyro element, it is necessary to make the exciting force acting on the detection vibrating arm larger and the amplitude larger. However, any of the above described vibration gyros in related art has only one vibration mode for detection, and it is not easy to improve the detection sensitivity by increasing the exciting force to the detection vibrating arm. Especially, as the vibration gyro element is made smaller in size, also the drive and detection vibrating arms are made smaller, and the improvement of the detection sensitivity by increasing the exciting force becomes more difficult.